High-substitution-degree hydroxypropyl cellulose and preparation method thereof

Abstract

The invention discloses high-substitution-degree hydroxypropyl cellulose and a preparation method thereof, and belongs to the technical field of cellulose production. Aiming at the problem that high-substitution-degree hydroxypropylcellulose is difficult to efficiently obtain in the prior art, the invention provides high-substitution-degree hydroxypropylcellulose and a preparation method thereof, and the preparation method comprises the following steps: alkalifying cotton powder, a solvent and alkali, adding an acidic material, then adding a phase transfer catalyst, dropwise adding an etherifying agent, carrying out first-stage reaction, then dropwise adding the etherifying agent, and carrying out second-stage reaction to obtain the high-substitution-degree hydroxypropylcellulose. And finally, neutralizing, washing, separating and drying to obtain the high-substitution-degree hydroxypropyl cellulose. According to the method, the phase transfer catalyst is introduced in the etherification reaction process to accelerate the reaction rate of a heterogeneous system, and meanwhile, the etherifying agent is dropwise added step by step, so that side reactions are reduced, the utilization rate of the etherifying agent is increased, and the content of hydroxypropoxy in the hydroxypropyl cellulose stably reaches 60% or above.

Description

Technical Field

[0001] The invention belongs to the technical field of cellulose production, and particularly relates to high-substituted hydroxypropyl cellulose and a preparation method thereof. Background Art

[0002] The current preparation methods of hydroxypropyl cellulose can be summarized into two methods:

[0003] One is a homogeneous preparation method, in which cellulose powder is dissolved in a suitable solvent (homogeneous system), reacted in an alkaline environment to prepare alkali cellulose, and then alkali cellulose and propylene oxide are etherified to obtain hydroxypropyl cellulose. For example, CN03128387.X adds propylene oxide to a homogeneous aqueous solution of NaOH / urea in cellulose, stirs the reaction at -6°C to 60°C for 10 minutes to 80 hours, and then adds acetic acid to neutralize the reaction solution to obtain hydroxypropyl cellulose, but the degree of substitution of hydroxypropyl cellulose obtained by this method is relatively low (MS is all below 1.73). In addition, CN202210522999.0 adds a cellulose raw material to a mixed solvent consisting of dimethyl sulfoxide and tetrabutylammonium fluoride trihydrate, heats to completely dissolve, obtains a cellulose solution, and obtains hydroxypropyl cellulose after alkalization and etherification. The degree of substitution of hydroxypropyl cellulose prepared by this method is generally low (MS is generally below 2.7), and hydroxypropyl cellulose with a high degree of substitution (MS greater than 3) can only be prepared when the reaction time is very long, such as the MS of 3.6 at a reaction time of 24h in Example 4 of CN202210522999.0. Therefore, the hydroxypropyl cellulose prepared by the homogeneous preparation method generally has a low degree of substitution, and it is difficult to prepare hydroxypropyl cellulose with a high degree of substitution. Although hydroxypropyl cellulose with a high degree of substitution can be prepared when the reaction time is very long, extending the reaction time will reduce production efficiency and easily lead to an increase in side reactions.

[0004] The other is a heterogeneous preparation method, in which cellulose powder is dispersed in a solvent, and alkalization and etherification reactions are carried out in a heterogeneous environment to prepare hydroxypropyl cellulose. For example, US3278520 and US3278521 first alkalize the cellulose, then squeeze the alkalized cellulose, and finally add the squeezed alkali cellulose to a diluent, and react with propylene oxide under heterogeneous conditions to obtain high-substituted hydroxypropyl cellulose. Although this method can be used to prepare high-substituted hydroxypropyl cellulose, it needs to react at 70°C for 16 hours, which is a long reaction time, low production efficiency, and a complicated squeezing process. In addition, long-term reaction at high temperature will lead to an increase in side reactions and a decrease in the utilization rate of the etherifying agent. Summary of the invention

[0005] In view of the problem that it is difficult to efficiently obtain high-degree-of-substitution hydroxypropyl cellulose in the prior art, the present invention increases the reaction rate and shortens the reaction time by adding a phase transfer catalyst during the preparation of hydroxypropyl cellulose, and reduces side reactions by dripping an etherifying agent in steps, thereby improving the utilization rate of the etherifying agent and achieving efficient preparation of high-degree-of-substitution hydroxypropyl cellulose.

[0006] The present invention first provides a method for preparing high-substituted hydroxypropyl cellulose, which comprises the following steps:

[0007] A. Evenly mix the refined cotton powder, the mixed solvent and the alkali, and alkalize under an inert atmosphere (the alkalization temperature is room temperature);

[0008] B. After the alkalization is completed, add an acidic substance to neutralize the alkali to the concentration required for the reaction, then add a phase transfer catalyst, raise the temperature to 60-80°C, and drop the etherifying agent. After the dropwise addition is completed, keep the temperature for reaction;

[0009] C. After the heat preservation reaction in step B is completed, the temperature is raised to 70-90°C, and the etherifying agent is added dropwise. After the addition is completed, the heat preservation reaction is carried out;

[0010] D. After the heat preservation reaction in step C is completed, the temperature is lowered to room temperature, an acidic substance is added to neutralize the remaining alkali, and the neutralized material is washed, separated and dried to obtain a highly substituted hydroxypropyl cellulose;

[0011] In step A, the mixed solvent is a mixture of a hydrocarbon organic solvent, a low-carbon alcohol and water;

[0012] In step B, the phase transfer catalyst is a polyether, a cyclic crown ether or a quaternary ammonium salt.

[0013] In the present invention, the etherifying agent is added dropwise step by step to reduce side reactions (avoid excessive concentration of the etherifying agent in the system) and improve the utilization rate of the etherifying agent. The temperature of the insulation reaction in step B needs to be controlled to be 10 to 30° C. higher than the temperature of the insulation reaction in step C.

[0014] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step A, the hydrocarbon organic solvent is an aromatic hydrocarbon or an aliphatic hydrocarbon.

[0015] Preferably, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step A, the aromatic hydrocarbon is benzene, toluene or xylene, and the aliphatic hydrocarbon is a saturated alkane of 6 to 9 carbon atoms (such as n-hexane, n-heptane, n-octane or n-nonane, or an isomer of n-hexane, n-heptane, n-octane or n-nonane, for example, 2-methylpentane, an isomer of n-hexane).

[0016] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step A, the low-carbon alcohol is a saturated alkyl alcohol having 3 to 5 carbon atoms.

[0017] Preferably, in the above method for preparing highly substituted hydroxypropyl cellulose, in step A, the low-carbon alcohol is propanol, isopropanol, n-butanol, tert-butanol or pentanol.

[0018] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step A, the mass ratio of the hydrocarbon organic solvent to the refined cotton powder is 7 to 11:1.

[0019] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step A, the mass ratio of the low-carbon alcohol to the refined cotton powder is 1 to 5:1.

[0020] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step A, the mass ratio of water to refined cotton powder is 0.05-0.5:1.

[0021] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step A, the base is sodium hydroxide or potassium hydroxide.

[0022] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step A, the mass ratio of the alkali to the refined cotton powder is 0.1-0.8:1.

[0023] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step A, the alkalization time is 0.1 to 5 hours.

[0024] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step B, the polyether is chain polyethylene glycol or chain polyethylene glycol dialkyl ether.

[0025] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step B, the cyclic crown ether is 18-crown 6, 15-crown 5 or cyclodextrin.

[0026] Among them, in the preparation method of the above-mentioned high-substituted hydroxypropyl cellulose, in step B, the quaternary ammonium salt is tetradecyltrimethylammonium chloride, trioctylmethylammonium chloride, tetrabutylammonium chloride, benzyltriethylammonium chloride (TEBA), dodecyltrimethylammonium chloride, tetrabutylammonium bromide (TBAB) or tetrabutylammonium hydrogen sulfate.

[0027] Preferably, in the above method for preparing highly substituted hydroxypropyl cellulose, in step B, the phase transfer catalyst is a cyclic crown ether.

[0028] More preferably, in the method for preparing the above-mentioned highly substituted hydroxypropyl cellulose, in step B, the phase transfer catalyst is 15 crown 5.

[0029] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step B, the mass ratio of the phase transfer catalyst to the refined cotton powder is 0.001-0.02:1.

[0030] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step B, the acidic substance is hydrochloric acid, sulfuric acid, phosphoric acid or acetic acid.

[0031] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step B, the molar ratio of the acidic substance to the alkali in step A is 0 to 0.9:1.

[0032] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step B, the etherifying agent is propylene oxide.

[0033] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step B, the mass ratio of the etherifying agent to the refined cotton powder is 1.5 to 5:1.

[0034] Wherein, in the above-mentioned preparation method of high-substituted hydroxypropyl cellulose, in step B, the dripping time of the etherifying agent is 0.5 to 1.0 h. The etherifying agent can be dripped through an isobaric feeding tank to control its dripping speed.

[0035] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step B, the insulation reaction time is 1.0 to 4.0 hours.

[0036] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step C, the etherifying agent is propylene oxide.

[0037] Wherein, in the above-mentioned preparation method of high-substituted hydroxypropyl cellulose, in step C, the dripping time of the etherifying agent is 0.5 to 1.0 h. The etherifying agent can be dripped through an isobaric feeding tank to control its dripping speed.

[0038] Wherein, in the preparation method of the above-mentioned high-substituted hydroxypropyl cellulose, in step C, the mass ratio of the etherifying agent to the refined cotton powder is 1.5-8:1. In steps B and C of the present invention, the mass ratio of the total amount of the etherifying agent added to the refined cotton powder is 3-13:1.

[0039] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step C, the insulation reaction time is 1.0 to 4.0 hours.

[0040] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step D, the acidic substance is hydrochloric acid, sulfuric acid, phosphoric acid or acetic acid.

[0041] Among them, in the preparation method of the above-mentioned highly substituted hydroxypropyl cellulose, in step D, the molar ratio of the acidic substance to the alkali in step A is 0.1-0.5:1. The molar ratio of the total amount of acidic substances added in steps B and D of the present invention to the alkali in step A is 0.1-1.4:1. When the total amount of acid is too little or too much, the remaining alkali or acid in the system can be removed in the subsequent washing process. The acidic substances added in steps B and D of the present invention can be the same acid or different acids; acids of different concentrations are suitable for the method of the present invention, and acids of different concentrations can be calculated according to their molar amounts.

[0042] Wherein, in the above-mentioned method for preparing highly substituted hydroxypropyl cellulose, in step D, the washing is 90-100° C. hot water washing; the number of hot water washing is 5-10 times.

[0043] The present invention also provides a high-substituted hydroxypropyl cellulose, which is prepared by adopting the preparation method of the high-substituted hydroxypropyl cellulose.

[0044] Beneficial effects of the present invention:

[0045] Aiming at the characteristic of slow reaction rate in the production process of highly substituted hydroxypropyl cellulose, the present invention introduces a phase transfer catalyst in the etherification reaction process to accelerate the reaction rate of the heterogeneous system and shorten the reaction time, thereby improving the production efficiency; at the same time, by dripping the etherifying agent in steps, the side reaction can be reduced (avoiding the excessive concentration of the etherifying agent in the system) and the utilization rate of the etherifying agent can be improved; thereby, the hydroxypropoxy content in the hydroxypropyl cellulose can be stably reached to more than 60% (equivalent to MS4.19), and can reach up to 73.2% (equivalent to MS7.63). DETAILED DESCRIPTION

[0046] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0047] Example 1

[0048] 1500g of refined cotton powder, 12000g of toluene, 3000g of n-butanol, 450g of water and 750g of sodium hydroxide were added to a 50L reactor, stirred and mixed, and the air in the reactor was replaced with nitrogen three times. The reactor was alkalized at 25°C for 1h. After the alkalization, 900g of acetic acid was added to neutralize part of the alkali, 15g of tetrabutylammonium chloride was added, the temperature was raised to 70°C, and 3000g of propylene oxide was added dropwise through an isobaric feeding tank. The dropping speed was controlled to make the etherification The agent was added in 0.5 hours, and the reaction was carried out at 70°C for 2.5 hours after the addition was completed; the temperature was raised to 85°C, and 2250g of propylene oxide was added dropwise through an isobaric feeding tank, and the dropping speed was controlled to make the etherifying agent added in 0.5 hours, and the reaction was carried out at 85°C for 2.5 hours after the addition was completed; after the reaction was completed, the temperature was lowered to room temperature, 225g of acetic acid was added for neutralization, and after neutralization, the material was added into 90°C hot water for 5 times of washing and separation, and a solid product was obtained after drying.

[0049] Example 2

[0050] 1500g of refined cotton powder, 16500g of xylene, 7500g of isopropanol, 450g of water and 750g of sodium hydroxide were added to a 50L reactor, stirred and mixed, and the air in the reactor was replaced with nitrogen three times. The reactor was alkalized at 25°C for 1h. After the alkalization, 342g of hydrochloric acid was added to neutralize part of the alkali, 15g of tetrabutylammonium chloride was added, the temperature was raised to 60°C, and 2250g of propylene oxide was added dropwise through an isobaric feeding tank. The dropping speed was controlled to etherify the reactor. The agent was added in 0.5 hours, and the reaction was carried out at 60°C for 2.5 hours after the addition was completed; the temperature was raised to 70°C, and 3000g of propylene oxide was added dropwise through an isobaric feeding tank, and the dropping speed was controlled to make the etherifying agent added in 0.5 hours, and the reaction was carried out at 70°C for 2.5 hours after the addition was completed; after the reaction was completed, the temperature was lowered to room temperature, 342g of hydrochloric acid was added for neutralization, and after neutralization, the material was added into 100°C hot water for 5 times of washing and separation, and a solid product was obtained after drying.

[0051] Example 3

[0052] 1500g of refined cotton powder, 12000g of benzene, 3000g of tert-butyl alcohol, 750g of water and 750g of sodium hydroxide were added to a 50L reactor, stirred and mixed, and the air in the reactor was replaced with nitrogen three times. Alkalization was performed at 25°C for 1h. After the alkalization, 900g of acetic acid was added to neutralize part of the alkali, 1.5g of polyethylene glycol 1000 was added, the temperature was raised to 80°C, and 7500g of propylene oxide was added dropwise through an isobaric feeding tank, and the dropping speed was controlled. The etherifying agent was added in 0.5 hours, and the mixture was reacted at 80°C for 1 hour after the addition was completed; the temperature was raised to 90°C, 1500g of propylene oxide was added dropwise through an isobaric feeding tank, and the addition speed was controlled to complete the addition of the etherifying agent in 0.5 hours, and the mixture was reacted at 90°C for 4 hours after the addition was completed; after the reaction was completed, the temperature was lowered to room temperature, 225g of acetic acid was added for neutralization, and after neutralization, the material was added into 100°C hot water for 7 washings, separation, and drying to obtain a solid product.

[0053] Example 4

[0054] 1500g of refined cotton powder, 10500g of n-heptane, 3000g of amyl alcohol, 450g of water and 1052g of potassium hydroxide were added to a 50L reactor, stirred and mixed, and the air in the reactor was replaced with nitrogen three times, and alkalized at 25°C for 1h; after the alkalization, 900g of acetic acid was added to neutralize part of the alkali, 30g of 15 crown 5 was added, the temperature was raised to 80°C, 2250g of propylene oxide was added dropwise through an isobaric feeding tank, the dropping speed was controlled so that the etherifying agent was added within 1 hour, and the reaction was carried out at 80°C for 3h after the dropping was completed; the temperature was raised to 90°C, 12000g of propylene oxide was added dropwise through an isobaric feeding tank, the dropping speed was controlled so that the etherifying agent was added within 1 hour, and the reaction was carried out at 90°C for 3h after the dropping was completed; after the reaction was completed, the temperature was lowered to room temperature, 225g of acetic acid was added for neutralization, and after neutralization, the material was added to 90°C hot water for 10 times of washing and separation, and a solid product was obtained after drying.

[0055] Example 5

[0056] 1500g of refined cotton powder, 12000g of n-hexane, 1500g of propanol, 75g of water and 1200g of sodium hydroxide were added to a 50L reactor, stirred and mixed, and the air in the reactor was replaced with nitrogen three times. The reaction mixture was alkalized at 25°C for 1h. After the alkalization, 1802g of acetic acid was added to neutralize part of the alkali, 22.5g of dodecyltrimethylammonium chloride was added, the temperature was raised to 70°C, and 4500g of propylene oxide was added dropwise through an isobaric feeding tank. The dripping temperature was controlled. The etherifying agent was added at an accelerated rate within 0.5 hours, and the mixture was reacted at 70°C for 3 hours after the addition was completed. The temperature was raised to 85°C, and 6000 g of propylene oxide was added dropwise through an isobaric feeding tank. The addition rate was controlled to complete the addition of the etherifying agent within 0.5 hours, and the mixture was reacted at 85°C for 2 hours after the addition was completed. After the reaction was completed, the temperature was lowered to room temperature, 225 g of acetic acid was added for neutralization, and after neutralization, the material was added into 90°C hot water for 5 washings and separations, and a solid product was obtained after drying.

[0057] Example 6

[0058] 1500g of refined cotton powder, 12000g of n-octane, 3000g of isopropanol, 450g of water and 150g of sodium hydroxide were added to a 50L reactor, stirred and mixed, and the air in the reactor was replaced with nitrogen three times, and alkalized at 25°C for 1h; after the alkalization, 7.5g of trioctylmethylammonium chloride was added, the temperature was raised to 70°C, 3000g of propylene oxide was added dropwise through an isobaric feeding tank, the dropping speed was controlled so that the etherifying agent was added within 0.5 hour, and the reaction was carried out at 70°C for 2h after the dropping was completed; the temperature was raised to 85°C, 4500g of propylene oxide was added dropwise through an isobaric feeding tank, the dropping speed was controlled so that the etherifying agent was added within 0.5 hour, and the reaction was carried out at 85°C for 3h after the dropping was completed; after the reaction was completed, the temperature was lowered to room temperature, 225g of acetic acid was added for neutralization, and after neutralization, the material was added to 90°C hot water for 5 washings and separations, and a solid product was obtained after drying.

[0059] Example 7

[0060] 1500g of refined cotton powder, 12000g of n-nonane, 3000g of tert-butyl alcohol, 450g of water and 750g of sodium hydroxide were added to a 50L reactor, stirred and mixed, and the air in the reactor was replaced with nitrogen three times. The reactor was alkalized at 25°C for 1h. After the alkalization, 1013g of acetic acid was added to neutralize part of the alkali, 15g of tetrabutylammonium hydrogen sulfate was added, the temperature was raised to 70°C, and 4500g of propylene oxide was added dropwise through an isobaric feeding tank, and the dripping speed was controlled to accelerate. The etherifying agent was added in 0.5 hours, and the mixture was reacted at 70°C for 4 hours after the addition was completed. The temperature was raised to 85°C, and 3000g of propylene oxide was added dropwise through an isobaric feeding tank. The dropping speed was controlled to complete the addition of the etherifying agent in 0.5 hours, and the mixture was reacted at 85°C for 1 hour after the addition was completed. After the reaction was completed, the temperature was lowered to room temperature, 113g of acetic acid was added for neutralization, and after neutralization, the material was added into 90°C hot water for 5 washings, separation, and drying to obtain a solid product.

[0061] Comparative Example 1

[0062] No phase transfer catalyst was added, and other conditions and experimental steps were completely consistent with those in Example 1.

[0063] Comparative Example 2

[0064] Without adding any phase transfer catalyst, the reaction was carried out at 70° C. for 4 h and at 85° C. for 4 h. Other conditions and experimental steps were completely consistent with those in Example 1.

[0065] Comparative Example 3

[0066] The two additions of propylene oxide were both made by direct addition without using an isobaric feeding tank to control the speed of propylene oxide addition. Other conditions and experimental steps were completely consistent with those in Example 1.

[0067] Table 1 Experimental conditions and product test results of each embodiment and comparative example

[0068]

[0069]

[0070] Note: The hydroxypropoxy content is determined by General Rule 0712 (Method 1, gas chromatography) of Part 4 of the 2020 edition of the Chinese Pharmacopoeia.

[0071] Examples 1 to 7 achieve efficient preparation of high-degree-of-substitution hydroxypropyl cellulose by using a variety of mixed solvents, phase transfer catalysts, etc. The prepared hydroxypropyl cellulose has a relatively high degree of substitution. The higher the degree of substitution, the better the solubility of the product in water, the more transparent the aqueous solution, and the requirements of high-degree-of-substitution hydroxypropyl cellulose can be met. In addition, it can be seen from Examples 1 to 7 that the use of cyclic crown ethers has the best effect, followed by the use of quaternary ammonium salts, and then the use of polyethers.

[0072] By comparing Example 1 with Comparative Example 1 and Comparative Example 2, it can be seen that when the reaction time and other conditions are the same (Example 1 and Comparative Example 1), adding an appropriate amount of phase transfer catalyst (tetrabutylammonium chloride) can accelerate the reaction rate and increase the hydroxypropoxy content of the product (from 51.5% to 59.8%); when no phase transfer catalyst is added, even if the reaction time is increased (Comparative Example 2, the total reaction time is increased to 8h), the hydroxypropoxy content (56.7%) cannot reach the result of Example 1 (59.8%). This shows that by adding a phase transfer catalyst, the reaction rate can be increased, the reaction time can be shortened, and the production efficiency can be improved.

[0073] By comparing Example 1 with Comparative Example 3, it can be seen that when other reaction conditions are exactly the same, changing the addition mode of propylene oxide from direct addition to dropwise addition through an isobaric feeding tank can increase the hydroxypropoxy content to a certain extent. This is because directly adding propylene oxide to the reactor will result in a very high concentration of propylene oxide, and propylene oxide will have more side reactions (such as propylene oxide reacting with water). However, slowly dropping propylene oxide through an isobaric feeding tank will not result in too high a concentration of propylene oxide in the reactant, which can reduce the occurrence of side reactions to a certain extent and improve the utilization rate of propylene oxide (etherifying agent).

Claims

1. A method for preparing a highly substituted hydroxypropyl cellulose, characterized in that: The following steps are involved: A. Evenly mix the refined cotton powder, the mixed solvent and the alkali, and alkalize under an inert atmosphere; B. After the alkalization is completed, add an acidic substance to neutralize the alkali to the concentration required for the reaction, then add a phase transfer catalyst, raise the temperature to 60-80°C, and drop the etherifying agent. After the dropwise addition is completed, keep the temperature for reaction; C. After the heat preservation reaction in step B is completed, the temperature is raised to 70-90°C, and the etherifying agent is added dropwise. After the addition is completed, the heat preservation reaction is carried out; D. After the heat preservation reaction in step C is completed, the temperature is lowered to room temperature, an acidic substance is added to neutralize the remaining alkali, and the neutralized material is washed, separated and dried to obtain a highly substituted hydroxypropyl cellulose; In step A, the mixed solvent is a mixture of a hydrocarbon organic solvent, a low-carbon alcohol and water; In step B, the phase transfer catalyst is a polyether, a cyclic crown ether or a quaternary ammonium salt.

2. The method for preparing highly substituted hydroxypropyl cellulose according to claim 1, characterized in that: At least one of the following is met: In step A, the hydrocarbon organic solvent is an aromatic hydrocarbon or an aliphatic hydrocarbon; preferably, the aromatic hydrocarbon is benzene, toluene or xylene, and the aliphatic hydrocarbon is a saturated alkane with 6 to 9 carbon atoms; In step A, the low-carbon alcohol is a saturated alkyl alcohol of 3 to 5 carbon atoms; preferably, the low-carbon alcohol is propanol, isopropanol, n-butanol, tert-butanol or pentanol; In step A, the mass ratio of the hydrocarbon organic solvent to the refined cotton powder is 7 to 11:1; In step A, the mass ratio of the low-carbon alcohol to the refined cotton powder is 1 to 5:1; In step A, the mass ratio of water to refined cotton powder is 0.05-0.5:

1.

3. The method for preparing highly substituted hydroxypropyl cellulose according to claim 1, characterized in that: At least one of the following is met: In step A, the base is sodium hydroxide or potassium hydroxide; In step A, the mass ratio of the alkali to the refined cotton powder is 0.1-0.8:1; In step A, the alkalization time is 0.1 to 5 hours.

4. The method for preparing highly substituted hydroxypropyl cellulose according to claim 1, characterized in that: At least one of the following is met: In step B, the polyether is chain polyethylene glycol or chain polyethylene glycol dialkyl ether; In step B, the cyclic crown ether is 18-crown-6, 15-crown-5 or cyclodextrin; In step B, the quaternary ammonium salt is tetradecyltrimethylammonium chloride, trioctylmethylammonium chloride, tetrabutylammonium chloride, benzyltriethylammonium chloride, dodecyltrimethylammonium chloride, tetrabutylammonium bromide or tetrabutylammonium hydrogen sulfate; In step B, the phase transfer catalyst is a cyclic crown ether; preferably 15-crown 5; In step B, the mass ratio of the phase transfer catalyst to the refined cotton powder is 0.001-0.02:

1.

5. The method for preparing highly substituted hydroxypropyl cellulose according to claim 1, characterized in that: At least one of the following is met: In step B, the acidic substance is hydrochloric acid, sulfuric acid, phosphoric acid or acetic acid; In step B, the molar ratio of the acidic substance to the base in step A is 0 to 0.9:1; In step B, the etherifying agent is propylene oxide; In step B, the mass ratio of the etherifying agent to the refined cotton powder is 1.5-5:1; In step B, the etherifying agent is added dropwise for 0.5 to 1.0 h; In step B, the insulation reaction time is 1.0 to 4.0 hours.

6. The method for preparing highly substituted hydroxypropyl cellulose according to claim 1, characterized in that: At least one of the following is met: In step C, the etherifying agent is propylene oxide; In step C, the etherifying agent is added dropwise for 0.5 to 1.0 h; In step C, the mass ratio of the etherifying agent to the refined cotton powder is 1.5-8:

1.

7. The method for preparing highly substituted hydroxypropyl cellulose according to claim 1, characterized in that: In step C, the insulation reaction time is 1.0 to 4.0 hours.

8. The method for preparing highly substituted hydroxypropyl cellulose according to claim 1, characterized in that: At least one of the following is met: In step D, the acidic substance is hydrochloric acid, sulfuric acid, phosphoric acid or acetic acid; In step D, the molar ratio of the acidic substance to the base in step A is 0.1-0.5:

1.

9. The method for preparing high-substituted hydroxypropyl cellulose according to any one of claims 1 to 8, characterized in that: In step D, the washing is performed by hot water washing at 90-100° C.; the number of hot water washing is 5-10 times.

10. The high-substituted hydroxypropyl cellulose prepared by the method for preparing high-substituted hydroxypropyl cellulose according to any one of claims 1 to 9.

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